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SBP, systolic blood pressure; DBP, diastolic blood pressure; SVR, systemic vascular resistance.

Serial measurements of venous oxygen saturation and lactate can also be
useful. ScvO2 , measured from the SVC-RA junction, <70% is evidence for
increased tissue oxygen extraction and inadequate oxygen delivery to meet
cellular metabolic demand. In shock, ScvO2 <70% should prompt consideration
to further improve oxygen delivery either through additional fluid administration,
vasoactive therapy, or an increase in arterial blood oxygen content (i.e., increase
inspired oxygen or RBC transfusion if hemoglobin is <10 g/dL). Although ScvO2
may also be low if metabolic demand is high (e.g., fever in sepsis), an ScvO2
<70% is evidence that oxygen delivery is lower than oxygen demand, and thus
the shock state remains. An elevated blood lactate concentration may also
indicate that tissue perfusion is inadequate, even if hypotension is not present (the
so-called cryptic shock ). Two randomized trials in adult sepsis have shown that a
10% to 20% decrease in lactate over 1 to 2 hours is associated with reduced
mortality, and observational pediatric studies have also demonstrated an
association between impaired lactate clearance and mortality. Blood pH and base
deficit may also be used as laboratory surrogates for improved tissue perfusion,
but these may be affected by hyperchloremia that commonly develops following
fluid resuscitation or changes in ventilation.